7238
J. Am. Chem. Soc. 1987, 109, 7238-7239
ditional studies are in progress to further characterize the thermochromism, the solution equilibrium, and the mechanism of the 119Sn-117Snscalar coupling in 1.
1.06
H2 ’
Acknowledgment. This work was supported by the National Science Foundation under Grant No. CHE-8517584 and by a Grant for Newly Appointed Young Faculty in Chemistry from the Camille and Henry Dreyfus Foundation Inc. (19) (a) Kiingensmith, K. A,; Downing, J. W.; Miller, R. D.; Michl, J. J. Am. Chem. SOC.1986,108,7438-7439. (b) Bigelow, R. W. Chem. Phys. Lett. 1986,126,63-68. (c) Schweizer, K. S. J . Chem, Phys. 1986,85, 1156-1183.
1.265(1) A O 1 W
Figure 1. The deltic acid molecule with atom nomenclature:
Deltic Acid, a Novel Compound
bond lengths (A), left, and angles (deg), right. Estimated standard deviations in parenthesis.
Dag Semmingsen* Institutt f o r Matematikk og Naturuitenskap Hagskolesenteret i Rogaland 4000 Stavanger, Norway Per Groth Kjemisk Institutt, Universitetet i Oslo 0315 Oslo 3, Norway Received June 8, 1987 Owing to their simplicity and attractive chemical structures, the cyclic oxocarbon acids (C,0,H2) and their conjugate bases, the oxocarbon anions (C,0,)2-, have been the subject of a number of experimental and theoretical investigations over the past several years.’-3 In particular it has been suggested that the oxocarbon anions constitute a series of aromatic compound^.^ Although this proposition has been questioned for the oxocarbons in general,5 there are theoretical arguments in favor of such a conception in case of the smallest member of the oxocarbon anions, the deltate i~n.~.~ While the structures of the other oxocarbon ring systems are fairly well documented,’-” no structure determination of the novel ring system in deltic acid has hitherto been reported. However, thorough investigations of the deltate ionI2 and deltic acidI3 by IR and Raman methods have been reported. Deltic acid and its lithium salt were first prepared by Eggerding and W e d 4 in 1976 by a method similar to that by Dehmlow,I5 and more recently in a total synthesis by Pericds and Serratosa,16 and is not easily accessible. In aqueous solutions deltic acid hydrolyzes with a ring opening, and although the deltate ion appears to be somewhat more stable and crystalline salts have been reported, crystals suitable for structural studies are difficult to obtain.I4 We wish to report the molecular and crystal structure of deltic acid as determined by X-ray analysis. A sample of the di-tert-butyl ester of the acid was kindly (1) For a review on oxocarbons, see: Oxocarbons; West, R., Ed.; Academic Press: NY, 1980; ISBN 0-12-744580-3. (2) Leibovici, C. J . Mol. Struct. 1972, 13, 185. (3) Farnell, L.; Radom, L.; Vincent, M. A. J . Mol. Struct. 1981, 76, 1. (4) West, R.; Niu, H.-Y.; Powell, D. L.; Evans, M. V. J . Am. Chem. SOC. 1960, 82, 6204.. (5) Aihara, J. J . Am. Chem. SOC.1981, 103, 1633. (6) Moyano, A,; Serratosa, F. J. Mol. Struct. 1982, 90, 131. (7) Macintyre, W. M.; Werkema, M. S. J. Chem. Phys. 1964, 42, 3563. (8) Baenziger, N. C.; Hegenbarth, J. J. J . Am. Chem. SOC.1964,86,3250. (9) Neuman, M. A. Diss. Abstr. 1966, 26, 6394. (10) Semmingsen, D. Acta Chem. Scand. 1973, 27, 3961. Semmingsen, D.; Hollander, J. F.; Koetzle, T. F. J . Chem. Phys. 1977, 66, 4405. (1 1) Semmingsen, D. Acta Chem. Scan. 1976, A30, 808. (12) West, R.; Eggerding, D.; Perkins, J.; Handy, D.; Tuazon, E. C. J. Am. Chem. SOC.1979, 101, 1710. (13) Lautit, A,; Lautit, M.-F.; Novak, A. Can. J . Chem. 1985, 63, 1394. Lautit, A,; Lautit, M. F.; Novak, A. J. Mol. Struct. 1986, 142, 29. (14) Eggerding, D.; West, R. J . Am. Chem. SOC.1976,98,3641; 1975.97, 207. (1 5) Dehmlow, E. V. Tetrahedron Letr. 1972, 127 1. (16) Pericis, M. A,; Serratosa, F. Tetrahedron Lett. 1977, 4437.
0002-7863/87/1509-7238$01.50/0
Figure 2. Stereo view of the unit cell.
supplied by Professor Serratosa, and crystals were grown from alcohol after direct crystal growth by slow hydrolysis of the ester in neat trifluoroacetic acid had failed. A crystal of the compound was subjected to a low-temperature X-ray analysis at the University of 0 ~ 1 0 . ~ ~ Bond lengths and angles are shown in Figure 1, while the arrangement of the molecules in the crystal is shown in Figure 2. The crystal structure of deltic acid corresponds closely to the model surmised by LautiE et al. on the basis of their IR and Raman spectroscopic investigation. The molecules are situated across a mirror plane in the crystal and thus have C,, symmetry. They are tied together in strings in the (120)-planes in a “dimeric” fashion resembling the well-known dimeric carboxylic acid units. However, each carbonyl group accepts two equivalent, strong hydrogen bonds (r(O--0) = 2.555 (1) A), which are almost perfectly linear (
